Cannula with a modular filter for filtering embolic material

ABSTRACT

A modular blood filter device and delivery system, comprising an arterial cannula with a modular filter device. The arterial cannula includes a distal end adapted to enter an artery, and a side port for receiving a modular filter cartridge. The modular filter cartridge includes a tubular cartridge, and a shaft having a handle on one end and an expandable filter device on the other end. The expandable filter device includes filter mesh and an expansion frame capable of assuming enlarged and contracted conditions. The shaft is inserted into the cartridge, thereby containing the expandable filter device therein. The cartridge may then be removably received by the side port on the cannula. The cannula may be introduced into a blood vessel, and the expandable filter device may be deployed through the cannula into the vessel. The expansion frame may be expanded to the enlarged condition to capture embolic material in the mesh, may be collapsed to the contracted condition, and may be removed from the vessel. The modular filter cartridge may be removed from the cannula, and a new modular filter cartridge may then be received therein.

The present invention relates generally to blood filter devices fortemporary placement in a blood vessel to capture embolic material, andmore particularly to a cannula with a modular filter device forplacement in a blood vessel to carry blood to the vessel and to entrapembolic material in the vessel, for example when delivering blood to theaorta from a bypass-oxygenator system during cardiac surgery. Thepresent invention also relates to methods for protecting a patient fromembolization which may be caused by procedures, such as incising,clamping and unclamping, which may dislodge atheromatous material froman artery.

BACKGROUND OF THE INVENTION

During cardiac surgery, it is often necessary to introduce a cannulainto an artery or other blood vessel. For example, an arterial cannulais typically introduced into the aorta to deliver blood from abypass-oxygenator system. Such a cannula generally includes a proximalend for receiving blood from a bypass-oxygenator machine, a distal endfor entry into an artery, and a lumen extending between the proximal anddistal ends.

One concern with such procedures is that calcified plaque or otherembolic material may be dislodged, particularly when clamping orunclamping arteries such as the aorta. See Barbut et al., "CerebralEmboli Detected During Bypass Surgery Are Associated With ClampRemoval," Stroke, 25(12):2398-2402 (1994), which is incorporated hereinby reference in its entirety. Such embolic material may traveldownstream, possibly becoming lodged in another portion of the bloodvessel or possibly reaching a vital organ, such as the brain, where thematerial can cause substantial injury to the patient.

For this reason, some arterial cannulas may include a blood filterdevice attached directly to them. For example, an expandable filterdevice may be mounted on the distal end of a cannula, allowing thefilter to capture any loose embolic material once the cannula isintroduced into the vessel. Generally, such devices include anexpandable frame, such as an inflation seal or an umbrella frame, and afilter mesh attached to the frame, the mesh being adapted to captureembolic material of a predetermined minimum size. The frame may beattached externally to the distal end, or alternatively, it may beretractably deployed from a lumen within the cannula.

The use of a cannula with such a filter device, however, may not be aseffective as desired. For example, because the filter is generallyattached to the distal end of the cannula, the filter may be exposedwithin the vessel for the entire duration of the procedure, sometimesseveral hours. Because of the length of time of most cardiac procedures,the filter mesh may eventually become clogged due to thrombus formationor buildup of embolic material, preventing the device from effectivelycapturing additional material and/or possibly impairing blood flowthrough the filter. If the filter is retractable, it may be closedwithin the vessel when it becomes clogged, but this prevents capture ofembolic material throughout the remainder of the procedure.

Accordingly, there is a need for a filter device for use with anarterial cannula that minimizes the exposure of the filter within ablood vessel, thereby reducing the risk of clogging the filter mesh.

SUMMARY OF THE INVENTION

The present invention is directed to a modular blood filter device and adelivery system for intermittently introducing the filter device into ablood vessel during an extended surgical procedure, and to methods forusing such a device. The present invention is also directed to anarterial cannula with modular filter device for temporary placement in ablood vessel to carry blood to the vessel and to entrap embolic materialin the vessel, for example when delivering blood to the aorta from abypass-oxygenator system during cardiac surgery.

Generally, an embodiment of an arterial cannula with modular filterdevice in accordance with the present invention comprises a cannula witha side port and a modular filter cartridge, the latter including anexpandable filter device and a tubular cartridge. The cannula is anelongate tubular member, having a distal end adapted to enter an artery,a proximal end adapted to receive blood from a bypass-oxygenatormachine, and a lumen which extends from the proximal end to the distalend. The cannual also includes a side port for receiving the modularfilter cartridge. The side port may be attached to or integrally formedon the outer surface of the cannula, possibly on the front (downstreamarea), back (upstream area) or side of the cannula. Preferably, the sideport is located adjacent the distal end of the cannula, for exampleabove the suture flange thereon. More preferably, the side port extendsdiagonally from the outer surface to facilitate directing the filterdevice towards the distal end of the cannula. A passage extends front heside port to the lumen in the cannula, or alternatively, may extenddistally from the side port along a wall of the cannula to an outlet onor adjacent the distal end of the cannula. The side port may include ahemostatic valve across the passage to provide a fluid-tight seal, yetallow a modular filter cartridge to be received in and removed from theside port.

An expandable filter device for use with embodiments of the presentinvention generally includes a semi-rigid shaft having a handle on itsproximal end and an expansion frame on its distal end. Filter mesh isattached to the expansion frame to provide an expandable filter capableof assuming enlarged and contracted conditions.

The expansion frame for the expandable filter may be self-expanding upondeployment, or may be controlled from the handle on the proximal end ofthe shaft. For example, the expansion frame may be formed from asuperelastic or shape memory material, such as a Nitinol ring, thatopens automically when deployed. Preferably, the ring includes kinkswhere the right is attached to the shaft, biasing the ring against thewall of a vessel, and maximizing the cross-section of the vesselintersected by the filter. Thus, once deployed, the ring automaticallyexpands across the vessel, opening the filter, such as a substantiallyconical mesh, to capture embolic material in the vessel.

Alternatively, the expansion frame may include an annular inflationseal, such as a silicon balloon, that may be filled with fluid to openthe mesh across the vessel into which the device is deployed. In thisembodiment, the shaft may include an inflation lumen extending betweenthe proximal and distal ends thereof for injecting and removing fluid.

The expansion frame may also be mechanically operated, such as by aguide wire and/or a spring connected to the expansion frame, generallycontrolled from the handle on the proximal end of the shaft. Forexample, the expansion frame may include a plurality of struts that maybe biased to the contracted condition, possibly using a shape memorymaterial or a spring. A ring attached to the struts may be directedaxially to expand and contract the struts respectively between theenlarged and contracted conditions.

In addition, the cannula with modular filter device also includes atubular cartridge into which the expandable filter device may beinserted. Generally, the cartridge is a tubular member providing ahemostatic seal between the shaft on the filter device and the side porton the cannula, or the cartridge may include a hemostatic valve toprovide a fluid-tight seal between the cartridge and the filter deviceinserted therein. The cartridge generally has a shape similar to theside port, as well as the shaft on the filter device. Preferably, thesecomponents have similar cross-sections, such as a substantially squareor rectangular shape, that limit the arterial cannula with modularfilter device to a predetermined assembled orientation that ensures thatthe filter device is deployed across the vessel when deployed. Thedistal end of the shaft on the expandable filter device is generallyinserted into the cartridge, such that the expansion frame and mesh aresubstantially contained within the cartridge, thereby providing amodular filter cartridge.

The modularity provided by the cartridge, combined with the side port onthe cannula, is an important feature of the present invention. Duringuse, the cannula may be introduced into a blood vessel, such as theaorta, using conventional procedures, a modular filter cartridgegenerally being provided in the side port prior to introduction of thecannula. Once the distal end of the cannula is in position within thevessel and the cannula is secured to the patient, the filter device maybe deployed into the vessel. The shaft of the filter device is directeddistally, causing the expandable filter on the distal end of the shaftto pass through the passage, through the lumen in the cannula and exitthe distal end of the cannula into the vessel. The expansion frame maythen expand automatically as it enters the vessel, or it may be expandedmechanically to its enlarged condition, opening the filter meshsubstantially across the vessel and capturing any embolic materialtraveling therethrough. At any time, the expansion frame may be closedto its contracted condition, either automatically by withdrawing theexpandable filter, or by mechanically closing it as described above,entrapping any embolic material captured by the mesh. The expandablefilter may be returned into the cartridge by pulling the shaftproximally, and the modular filter cartridge may then be removed fromthe side port if desired. A new modular filter cartridge may be insertedinto the side port, and a new filter may then be introduced into thevessel.

The ability to replace the filter at any time during a procedure isparticularly useful in cardiac surgery. For example, the cannula andfilter may be deployed as described above within the aorta. The aortamay then be clamped in preparation for a bypass procedure, possiblydislodging embolic material from the wall of the aorta and travelingdownstream. With the filter deployed, however, embolic material releasedduring this action may easily be captured by the filter device. Once theaorta is clamped, the risk of embolic material breaking loose issubstantially reduced, and so the filter may be removed withoutsubstantial concern about embolic material escaping to other areas ofthe patient.

Later in the surgery, a new filter may be introduced into the aorta whenthe risk of embolic material becoming dislodged is again increased, asfor example when the aorta is unclamped. Because a new filter may bedeployed, any embolic material that is dislodged has a much greaterlikelihood of being captured by the filter without substantiallyimpairing blood flow through the vessel. Thus, a cannula with modularfilter device in accordance with the present invention may moreeffectively capture and remove embolic material released during extendedprocedures, such as coronary bypass surgery.

Accordingly, a principal object of the present invention is to provide amodular blood filter device and delivery system that allows the filterto be decoupled from the delivery system when not needed, and thatallows a new filter to be introduced to more effectively capture embolicmaterial within the vessel, such as during an extended surgicalprocedure.

It is also an object of the present invention to provide an arterialcannula with modular filter device that substantially minimizes thelikelihood of the blood filter becoming clogged and ineffective duringuse.

Additional objects and features of the present invention will becomeapparent from consideration of the following description taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an embodiment of an arterial cannula receivinga modular filter cartridge therein.

FIG. 2 is a partially cut-away side view of the arterial cannula of FIG.1 with the modular filter cartridge received therein, showing the filterpartially deployed.

FIG. 3 is another partially cut-away side view of another preferredembodiment of an arterial cannula with the modular filter cartridgereceived therein, showing an alternative arrangement of the deployedfilter.

FIGS. 4 and 5 are side views of the distal end of an arterial cannula inaccordance with the present invention introduced into a blood vessel,showing the side port located on the back and on the front,respectively, of the cannula.

FIG. 6 is a perspective view of a distal portion of an arterial cannulafrom a generally upstream position, showing a conical filter devicefully deployed.

FIG. 7 is a perspective view of the distal end of the arterial cannulaof FIG. 6 from a generally downstream position.

FIG. 8 is a back view of an embodiment of an expandable filter device inaccordance with the present invention.

FIG. 9 is a side view of the expandable filter device of FIG. 8.

FIG. 10 is a cross-section of a support strut taken along line 10--10 ofFIG. 9, including an inflation seal for engaging the wall of a vesselwhen the expandable filter device is deployed.

FIG. 11 is a cross-section of an alternative embodiment of a supportstrut taken along line 10--10 of FIG. 9, including a self-expanding foamfor engaging the wall of a vessel.

FIGS. 12 and 13 are side views of alternative embodiments of expansionframes for use in an expandable filter device in accordance with thepresent invention.

FIG. 14 is a side view of a spring-activated expansion frame for anexpandable filter device in accordance with the present invention.

FIG. 15 is a side view of an embodiment of an expansion frame having"sausage" struts and an inflation seal.

FIGS. 16 and 17 are perspective views of the distal portion of a cannulawith modular filter device in accordance with the present invention,with the expandable filter device deployed.

FIG. 18 is a perspective view of a distal portion of an arterial cannulawith modular filter device, showing the modular filter cartridge afterbeing received in the arterial cannula.

FIG. 19 is a perspective view of a distal portion of the arterialcannula with modular filter device of FIG. 18, prior to the modularfilter cartridge being received in the arterial cannula.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the drawings, FIGS. 1-5 and 16-19 show embodiments of anarterial cannula with modular filter device 10 in accordance with thepresent invention. As shown in FIGS. 18 and 19, the device 10 generallyincludes three components, namely a cannula 20, a tubular cartridge 42and an expandable filter device 60, the latter two components togetherdefining a modular filter cartridge 40.

The cannula 20 is an elongate tubular member 22, having a proximal end(not shown), a distal end 24, and a lumen 26 which extends between theproximal and distal ends 24. The proximal end is adapted for receivingblood from a bypass-oxygenator machine (not shown). The distal end 24has a tapered, curved and/or rounded end adapted to enter an artery (notshown), and includes an outlet 28 communicating with the lumen 26. Thecannula 20 may be formed from a substantially rigid material.

The cannula 20 includes a side port 32 for receiving the modular filtercartridge 40. The side port 32 may be attached to or integrally formedon the cannula 20, possibly on the front (downstream area), back(upstream area) or side of the cannula, as shown, for example, in FIGS.4 and 5. Preferably, the side port 32 is located adjacent the distal end24 of the cannula 20 above a suture flange 30 thereon, and extendsdiagonally from the cannula 20. A passage 34 extends from the side port32 to the lumen 26 in the cannula 20, as shown in FIG. 2. Alternatively,the passage 34 may communicate with the lumen 26 of the cannula 20, andthe distal end 24 of the cannula 20 may include a separate filter outlet29, as shown in FIG. 3, or the passage 34 may be isolated from the lumen26 and extend distally from the side port 32 along a wall of the cannula20 to a filter outlet (not shown) on or adjacent the distal end 24 ofthe cannula 20. Preferably, the side port 32 also has a predeterminedcross-sectional configuration corresponding to the modular filtercartridge 40, as explained below. Optionally, the side port 32 mayinclude a hemostatic valve (not shown) across the passage 34, providinga fluid-tight seal that prevents fluid flow out of the passage 34 fromthe lumen 26 of the cannula 20, yet allows the modular filter cartridge40 to be received in and removed from the side port 32.

The tubular cartridge 42 is generally an elongate tubular member havinga proximal end 44, a distal end 46 and a channel (not shown) forreceiving the filter device 60. The cartridge 42 facilitates the modularnature of the device 10, providing a hemostatic seal between the filterdevice 60 and the side port 32 on the cannula 20. The cartridge 42 mayhave an outer wall 48 shaped similarly to the passage 34 in the sideport 32 as shown in FIGS. 18 and 19, thereby providing a fluid-tightseal when the modular filter cartridge 40 is received in the side port32. The channel in the cartridge 42 may also have a shape similar to thefilter device 60 to provide a fluid-tight seal between the cartridge 42and the filter device 60. Alternatively, a hemostatic valve (not shown)may be provided across the channel, for example at the proximal end 44of the cartridge 42 to provide a fluid-tight seal, yet allow the filterdevice 60 to be slidably received in and possibly removed from thecartridge 42. Preferably, the cartridge 42 is provided from moldedplastic materials that provide a hemostatic seal when the outer wall 48of the cartridge 42 slidably engages the passage 34 in the side port 32,and when the shaft 62 of the filter device 60 slidably engages thechannel in the cartridge 42.

Referring to FIGS. 16-19, the expandable filter device 60 generallyincludes a shaft 62, a handle 68 and an expandable filter 70. The shaft62 is generally an elongate member, having the handle 68 on its proximalend 64 and the expandable filter 70 on its distal end 66. Optionally,the shaft 62 may include a passage 65, such as for an inflation lumen ora mechanical control apparatus for the expandable filter 70, extendingbetween the proximal end 64 and the distal end (not shown). The shaft 62may be provided from a resilient semi-rigid material that is biased to aparticular shape, for example to remain substantially straight, but issufficiently flexible to follow the contour of the passage 34 and/or thelumen 26 in the cannula 20. Exemplary materials include plastic ormetal. Generally, the shaft 62 may have a cross-section corresponding tothe channel in the cartridge 42, thereby providing a hemostatic sealthat prevents flow of fluid through the channel, although alternatively,the cartridge 42 may include a separate seal as described above, or theshaft 62 may include a seal (not shown).

Preferably, the cross-sections of the side port 32, the cartridge 42 andthe shaft 62 have a substantially square, rectangular or other similarshape. The corresponding shape preferably limits the device 10 to beingassembled in a single orientation. This may be particularly important toensure that the expandable filter 70 is deployed within a blood vesselsuch that it intersects the vessel, and substantially engages the wallof the vessel to effectively capture embolic material. The side port 32also helps orient the surgeon using the device 10 with respect to thevessel. For example, with the side port 32 on the side of the cannula 20as shown in FIGS. 16 and 17, the surgeon may orient the side port 32perpendicular to the vessel to ensure that the outlet is directeddownstream and that the filter is oriented for proper deployment.

Turning now to FIGS. 8 and 9, an embodiment of an expandable filter 70is shown that may be provided on or near the distal end 66 of the shaft62. The expandable filter 70 generally includes an expansion frame 72capable of assuming enlarged and contracted conditions, and filter mesh80. Preferably, the expansion frame 72 includes a plurality of struts 74that may be expanded and contracted to define respectively the enlargedand contracted conditions. Filter mesh 80 is attached to the struts 74,75 of the expansion frame 72. For a complete explanation of the designand construction of a filter mesh for use in accordance with the presentinvention, the reader is referred to Barbut et al., U.S. applicationSer. No. 08/553,137, filed Nov. 7, 1995, Barbut et al., U.S. applicationSer. No. 08/580,223, filed Dec. 28, 1995, Barbut et al., U.S.application Ser. No. 08/584,759, filed Jan. 9, 1996, Barbut et al., U.S.application Ser. No. 08/640,015, filed Apr. 30, 1996, Barbut et al.,U.S. application Ser. No. 08/645,762, filed May 14, 1996, and Lyon &Lyon Docket No. 224/194, filed Apr. 16, 1997. The disclosure of thesereferences and any others cited herein are expressly incorporated hereinby reference.

In the preferred embodiment of FIGS. 8 and 9, the struts 74, 75 may openautomatically into a substantially hemispherical shape when deployed,for example, by providing them from plastic, spring stainless steel, ora superelastic and/or shape memory material, such as Nitinol, that isbiased to expand to define the hemispherical shape. Stabilizers 76 maybe provided to stabilize the expansion frame 72, or may be omitted ifthe bias of the struts 74, 75 provides sufficient stability. Inaddition, the struts 74, 75 may be attached to the shaft 62 using hingedjoints to facilitate expanding and contracting the expansion frame 72.

The open end struts 75 may also include seals for engaging the wall of ablood vessel to substantially minimize embolic material traveling aroundthe periphery of the deployed expandable filter 70. For example, asshown in FIG. 10, the struts 75 may include a silicone or urethaneballoon 76 attached along their length that may be inflated from a lumen(not shown) extending between the struts 75 and the shaft 62. Theballoon 76 may also be used to expand the expansion frame 72 to itsenlarged condition if the struts 74, 75 are unbiased or are biased tothe contracted condition. Alternatively, as shown in FIG. 11, the struts75 may include a self-expanding foam 82, such as silicone, that willexpand when the expandable filter 70 is deployed to substantially engagethe wall of the vessel.

Alternatively, as shown in FIG. 3, the struts 74 may have anumbrella-like configuration, which may be particularly useful when theexpandable filter 70 is deployed out a filter outlet 29 on the back(upstream side) of the cannula 20. The struts 74 may be biased to expandto the enlarged condition. To remove the expandable filter 70, the shaft62 may be pulled proximally, closing the struts 74 as they enter thefilter outlet 29.

In another preferred embodiment, such as that shown in FIGS. 6 and 7,the expansion frame 72 is a self-expanding ring 73 formed from springstainless steel or a superelastic and/or shape memory material, such asNitinol. The ring 73 may be compressed for insertion into the cartridge42, but, because of the shape memory of the material, it is biased toopen automatically into an annular shape when the expandable filter 70is deployed. Preferably, the ring 73 also includes a kink 75 adjacentthe distal end 66 of the shaft 62 to bias the ring 73 against the wallof the vessel, and maximize the cross-section of the vessel intersectedby the expandable filter 70. Without the kink 75, the ring may deformslightly, creating an imperfect circular cross-section that may allowembolic material to escape around the periphery of the deployedexpandable filter 70. The filter mesh 80 attached to the ring 75preferably has a substantially conical shape, such that when the ring 75expands across the vessel, the mesh 80 is pulled open downstream byblood flow in the vessel to capture any embolic material travelingthrough the vessel.

Alternatively, as shown in FIG. 15, the expansion frame 72 may include aring 75 having a "sausage" configuration, that is, having hinges ordimples on several locations around the ring 75, allowing the ring 75 toenlarge and contract more easily, and conform tightly to vessel lumentopography. Preferably, this embodiment also includes a balloon 84attached around the periphery of the ring 75 to guide the ring 75 toassume a substantially round configuration when the balloon 82 isinflated.

In still another preferred embodiment, a mechanically-operated expansionframe 72 may be provided. For example, the expansion frame 72 of FIGS.12 and 13 includes a ring 78 to which one end 74a, 75a of the struts 74,75 are attached. The ring 78 may be slidable axially in relation to theshaft 62, for example by use of a control wire or sleeve (not shown) toexpand and contract the struts 74, 75. Alternatively, the ring 78 may betwisted radially to open and/or close the struts 74, 75.

As shown in FIG. 14, a spring 79 may be provided between the ends 74a,75a, 74b, 75b of the struts 74, 75. The spring 79 may be compressed byuse of a control wire or like apparatus (not shown) to expand the struts74, 75 to the enlarged condition. When the filter 70 is to be removed,the spring 79 biases the expansion frame 72 to compress the struts 74,75 to the contracted condition, entrapping embolic material in the mesh80.

Alternatively, the open end struts 75 may themselves be provided fromcompressed springs (not shown), thus biasing them to the contractedcondition. Such struts may conform more easily to the shape of the wallof the vessel than solid struts.

Generally, as shown in FIG. 19, the cannula 20 and the modular filterdevice 40 are furnished separately, although alternatively, the device10 may be provided preassembled as in FIG. 18. The cartridge 42 andfilter device 60, however, are generally preassembled, thereby providingthe modular filter cartridge 40. This is accomplished by compressing theexpandable filter (not shown) and directing the distal end (not shown)of the shaft 62 into the channel (not shown) in the cartridge 42, suchthat the expansion frame and mesh (not shown) are substantiallycontained within the cartridge 42.

Prior to use, the modular filter cartridge 40 may be inserted into theside port 32 of the cannula 20, as shown in FIG. 18. The distal end 24of the cannula 20 may then be introduced into a blood vessel 100, suchas the aorta, using conventional procedures, as illustrated in FIGS. 4and 5, allowing blood to be carried into the vessel 100 from the lumen26. Once the distal end 24 of the cannula 20 is in position within thevessel 100 and the cannula 20 is secured to the patient, such as usingthe suture flange 30, the expandable filter may be deployed into thevessel, as shown in FIGS. 16 and 17.

As shown in FIGS. 2 and 3, the shaft 62 of the filter device 60 may bedirected distally to deploy the expandable filter 70 on its distal end66. This causes the expandable filter 70 to pass through the passage 34,through the lumen 26 in the cannula 20 and to exit the distal end 24 ofthe cannula 20 either through the outlet 28 (FIG. 2) or the filteroutlet 29 (FIG. 3), into the vessel (not shown in FIGS. 2 and 3). Theexpansion frame 72 may open automatically, or may be mechanicallyexpanded to its enlarged condition, thereby opening the filter mesh 80substantially across the vessel and capturing any embolic materialtraveling therethrough. At any time, the expansion frame 72 may beclosed to its contracted condition, entrapping any embolic materialcaptured by the mesh 80, and the expandable filter 70 withdrawn bypulling proximally on the shaft 62. The expandable filter 70 may bereturned into the cartridge 42, which may then be removed from the sideport 32. A new modular filter cartridge 40 may be inserted into the sideport 32 at any time thereafter, allowing a new expandable filter 70 tobe introduced into the vessel, as desired during a surgical procedure.

The modular filter device and delivery system in accordance with thepresent invention is particularly useful in cardiac surgery. A cannulawith modular filter as described above may be deployed within the aorta,for example, upstream of the carotid arteries. The aorta may be clampedupstream of the cannula with modular filter in preparation for a bypassprocedure. This clamping generally substantially increases the risk ofembolic deposits breaking loose from the wall of the aorta and travelingdownstream. With the filter deployed, however, embolic materialdislodged during this action may be captured by the filter device. Oncethe aorta is clamped, the risk of further embolic material beingdislodged may be substantially reduced, and so the filter may be removedwithout substantial concern about embolic material escaping and possiblyinjuring the patient.

Later in the surgery, a new filter device may be introduced through thecannula into the aorta prior to any action which may substantiallyincrease the risk of further embolic material breaking loose, such aswhen the aorta is unclamped. Because a new filter may be deployed, anyembolic material that is dislodged may be captured more effectively, asopposed to a filter which must remain in the aorta throughout theprocedure which may become clogged and impair blood flow through thevessel.

Similarly, the cannula with modular filter may be used to captureembolic material when balloon occlusion is used instead of clamping toclose the aorta in bypass procedures. In this procedure, the occlusionballoon may be provided on the same cannula providing the modularfilter. Alternatively, a catheter may be introduced into the aortaupstream of the bypass cannula, possibly through a cardioplegic cannula.A filter may be deployed prior to inflation of the occlusion balloon,thereby capturing any embolic material released by the balloon as itengages the walls of the aorta. This procedure may be slightlydisfavored, however, since it may reduce the work space available forthe bypass cannula and modular filter device.

An important feature of the present invention is that the filter may beplaced immediately downstream of the location which is likely togenerate emboli within the bloodstream, such as within the aorta. Inaddition, a filter device in accordance with the present may moreeffectively capture embolic material, because the expansion frame in theenlarged substantially engages the wall of the vessel extending the meshacross the vessel, and because the expansion frame may be closed beforeremoval, entrapping the captured material. Thus, the arterial cannulawith modular filter device in accordance with the present invention maymore effectively capture and remove embolic material released duringextended procedures, such as coronary bypass surgery, without cloggingthe filter and impairing blood flow through the vessel.

In some cases, it may desirable to provide the filter upstream of thecannula outlet through a separate filter outlet, as shown in FIG. 3. Forexample, this embodiment eliminates filtering the bypass blood which mayaccelerate clogging of the filter. It also may allow a variety of nozzledesigns to be provided on the cannula, without concern that the outletmay be partially obstructed by the shaft of the filter device, as mayoccur with filters deployed through the cannula outlet.

While the invention is susceptible to various modifications, andalternative forms, specific examples thereof have been shown in thedrawings and are herein described in detail. It should be understood,however, that the invention is not to be limited to the particular formsor methods disclosed, but to the contrary, the invention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the appended claims.

What is claimed is:
 1. A method of temporarily filtering embolic material from the blood in a blood vessel, said method comprising the steps of:providing a cannula having an outer surface, a distal end adapted to enter an artery, a proximal end adapted to receive blood from a bypass-oxygenator machine, a lumen which extends from the proximal end to the distal end, and a port on the outer surface of the cannula, said port having a passage therein extending distally into the cannula; providing a modular filter cartridge removably insertable into the port, said modular filter having an expandable filter therein, the expandable filter capable of assuming enlarged and contracted conditions; introducing the distal end of the cannula into a blood vessel; inserting the modular filter into the port on the cannula; advancing the expandable filter through the cannula into the blood vessel; deploying the expandable filter within the vessel; and removing the expandable filter from the vessel, wherein embolic material is generated and filtered before the expandable filter is removed from the vessel.
 2. The method of claim 1, comprising the additional step of removing the modular filter from the port.
 3. The method of claim 2, comprising the additional step of inserting a second modular filter into the port of the cannula after the step of removing the modular filter.
 4. The arterial cannula of claim 1, wherein the modular filter cartridge provides a hemostatic seal between the expandable filter and the port.
 5. The arterial cannula of claim 1, wherein the modular filter cartridge comprises:a shaft having a proximal end and a distal end; an expansion frame mounted on the distal end of the shaft which is expandable between a contracted and enlarged condition; and a filter mesh attached to the expansion frame.
 6. The arterial cannula of claim 1, wherein the passage in the filter port communicates with the lumen in the cannula.
 7. The arterial cannula of claim 5, wherein the expansion frame comprises a substantially circular belt of self-expanding material.
 8. The arterial cannula of claim 7, wherein the self-expanding material is spring stainless steel.
 9. The arterial cannula of claim 7, wherein the self-expanding material is Nitinol.
 10. A medical device for filtering embolic material, comprising:a cannula having an outer surface, a distal end adapted to enter an artery, the distal end having a distal opening, a proximal end adapted to receive blood from a bypass-oxygenator machine, and a lumen which extends from the proximal end to the distal end and communicates with the distal opening; a port on the outer surface of the cannula and located adjacent a distal region of the cannula, the port having a passage therein extending distally and communicating with a distal opening in the port, said passage separated from the lumen of the cannula; and a modular filter cartridge removably insertable through the passage of the port, wherein the modular filter cartridge comprises:a shaft having a proximal end and a distal end, wherein the distal end of said shaft is configured to be insertable through the passage of said port while the proximal end of said shaft extends outside of said port; an expansion frame mounted on the distal end of the shaft, wherein said frame is expandable between a contracted condition and an enlarged condition, wherein said expansion frame is deployable through the distal opening of said passage of said port; and a filter mesh attached to the expansion frame.
 11. The medical device of claim 10, wherein the modular filter cartridge provides a hemostatic seal between the expandable filter and the port.
 12. The medical device of claim 10, wherein the expansion frame comprises a substantially circular belt of self-expanding material.
 13. The medical device of claim 12, wherein the self-expanding material is spring stainless steel.
 14. The medical device of claim 12, wherein the self-expanding material is Nitinol or shape-memory material.
 15. The medical device of claim 10, wherein the expansion frame comprises an umbrella structure.
 16. The medical device of claim 10, wherein the expansion frame comprises a plurality of struts.
 17. The medical device of claim 10, wherein the expansion frame comprises a plurality of compressed springs.
 18. The medical device of claim 10, wherein the cannula further includes a suture flange. 